VEGETABLE AND FIELD CBOPS 



195 



neath. This, the summer stage, is chiefly responsible for 

 the hibernation of rust in the east. Later in the season 

 the sori become black 

 instead of rusty col- 

 ored, thus constituting 

 the winter stage of the 

 rust. 



In the spring still an- 

 other stage, the spring 

 stage, may occasionally 

 be seen, though it is 

 rare east of the Rocky 

 Mountains. This con- 

 sists of small, oval, pale 

 spots upon the branches 

 or leaves. In the cen- 

 ters of these spots small 

 round pustules develop 

 in concentric lines. 

 Soon each pustule 

 opens, constituting a 

 very minute cup which 

 is sunken into the leaf. 

 From these cups issues 

 a powder quite similar 

 to that from the sori of 



the summer stage, though more orange in color. All three 

 stages of rust — spring, summer, and winter — may occur 

 simultaneously upon the same plant. 



The disease spreads rapidly throughout the field during 

 the spring and summer stages. The winter stage is the 



Fig. 86. — Sori of the asparagus rust upon the 

 stems, enlarged. Original. 



